Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$247.73	12.329%	$278.2726	$278.27	$278.25	$278.30
Purchase #2	$152.97	12.688%	$172.3788	$172.38	$172.40	$172.40
Purchase #3	$97.93	13.419%	$111.0712	$111.07	$111.05	$111.10
Purchase #4	$83.53	4.599%	$87.3715	$87.37	$87.35	$87.40
Purchase #5	$219.63	4.388%	$229.2674	$229.27	$229.25	$229.30
Purchase #6	$233.86	12.191%	$262.3699	$262.37	$262.35	$262.40
Purchase #7	$238.26	9.339%	$260.5111	$260.51	$260.50	$260.50
7 purchase totals =	$1,273.91		$1,401.2425	$1,401.24	$1,401.15	$1,401.40